1. Field of the Invention
The present invention relates to a joint between a fiber reinforced resin and a metal.
2. Description of the Related Art
Fiber reinforced plastics (FRPs) are today used widely in structural members for aircraft, vehicles, ships, and general industrial instruments. For example, a known structural member is formed by impregnating a woven fabric, which is constituted by inorganic reinforcing fibers such as carbon fibers or glass fibers that are disposed in crisscross and interwoven, with a resin such as epoxy resin, and then hardening the resin.
In many cases, however, structural members are not formed entirely from fiber reinforced plastics, and a metallic material must be applied partially thereto.
It is therefore necessary to join the fiber reinforced plastic and the metallic material with a high degree of strength. In techniques proposed in the related art, as described in Japanese Unexamined Utility Model (Registration) Application Publication (JP-UM-A) No. S63-178126 and Japanese Examined Patent Publication (JP-B) No. S61-009135, and Japanese Unexamined Patent Application Publication (JP-A) No. 2001-032819, the fiber reinforced plastic is adhered directly to the metallic material, thereby eliminating the need for a fastening tool, and as a result, a reduction in weight and so on are achieved.
In the case where two members are joined by adhesion, if end surfaces of the two members are mated such that a resulting mating surface serves alone as an adhesion surface, the adhesion surface is small, and therefore a large degree of strength cannot be expected from a resulting joint structure.
A joint structure described in JP-UM-A No. S63-178126 employs a step-shaped joint surface obtained by forming complementary step structures on each of the end portions of two members to be joined. As a result, an adhesion surface having a large surface area is secured on a step surface that is perpendicular to the mating surface.
A joint structure described in JP-B No. S61-009135 employs a multi-step-shaped joint surface in a tube material. Further, JP-B No. S61-009135 describes a structure in which the step-shaped joint surfaces are superposed in two layers (see FIG. 3 of JP-B No. S61-009135). In this structure, an end portion of a metallic material formed in a tapered step shape is inserted into a groove formed in a shallow step shape that opens onto an end surface of a fiber reinforced plastic.
In a joint structure described in JP-A No. 2001-032819, a fiber reinforced plastic and a metallic material are disposed so as to overlap partially and wound together in a shaft material with axial direction ends thereof arranged diagonally. Thus, the two materials are superposed alternately in a plurality of layers on a cross-section passing through an axis thereof.
According to the technique described in JP-A No. 2001-032819, however, although the two materials can be superposed alternately to form a multi-layer structure, it is only possible to form a roll-shaped pipe material, and a planar structure or a structure having a desired curve cannot be formed. Moreover, a step-shaped joint surface, and in particular a multi-step-shaped joint surface, cannot be formed. Furthermore, as the two materials are wound, a region in which the materials are superposed gradually becomes misaligned in the axial direction such that the region increases in length. It is difficult to form another structure simultaneously in a structural portion used as a joint. Therefore, when the joint structure increases in size, a degree of design freedom is restricted correspondingly. As a result, application locations for the joint structure become limited, which is undesirable.
Furthermore, the technique described in JP-UM-A No. S63-178126 relates to a joint structure formed by superposing a single layer of fiber reinforced plastic and a single layer of metallic material. In the technique described in JP-B No. S61-009135, the metallic material is not provided in two or more layers.
Hence, with the conventional techniques described above, it is difficult to obtain a structure that is formed by alternately superposing at least two layers each of a fiber reinforced plastic and a metallic material and has a planar shape or a desired curved shape. Moreover, limitations occur naturally in a layer thickness of the layers relative to an overall required thickness, making it difficult to increase the number of layers.
Therefore, as shown in FIG. 8, for example, the inventors have developed a joint structure 100 for a fiber reinforced resin and a metal which is formed by laminating a plurality of single elements 103, each constituted by a metallic material 101 that includes a step-shaped structure having an end portion that gradually becomes thinner in a direction of an end surface of the end portion so as to form a step-shaped joint surface, and a fiber reinforced plastic 102 laminated such that an end portion thereof covers the step-shaped structure smoothly. With this joint structure, a number of steps of the step-shaped joint surface can be increased. Moreover, a number of fiber reinforced resin layers and metal layers laminated alternately via the step-shaped joint surface can be increased easily while suppressing an overall thickness.
Further, to increase the joint strength, the inventors have investigated a technique of adhering the metallic material 101 and the fiber reinforced plastic 102 by thermally curing each element 103, and then forming a welding portion 104 on each joint surface by welding adjacent metallic materials 101.
In the joint structure 100 shown in FIG. 8, however, resin that flows out of the fiber reinforced plastic 102 when the plurality of laminated elements 103 are thermally cured may infiltrate an entire inter-layer region. As a result, a defect such as porosity may occur when the metallic materials 101 are welded.